1. Field of the Invention
The present invention relates generally to a magnetic erasing transducer head and more particularly to a rotary magnetic erasing transducer head suitable for use on various kinds of video tape recorders (VTRs).
2. Description of the Prior Art
As, for example, shown in FIG. 1, when a pair of rotary magnetic heads H.sub.A and H.sub.B are mounted on a rotary drum 1 with an angular distance of approximately 180.degree. therebetween and a helical video track is formed on a magnetic tape 2 which is wound around the rotary drum 1 with a wrapping angle of approximately 180.degree., it is proposed to erase such video track by using a rotary magnetic head.
By way of example, as shown in FIG. 1, a rotary erasing head H.sub.E is mounted on the rotary drum 1 with a predetermined angular distance relative to one recording and/or reproducing rotary magnetic head H.sub.A by which a plurality of tracks can be erased simultaneously.
If the frequency of an erasing signal which is supplied to the rotary erasing head is high (a practical value is different depending on the kinds of the VTR sets), due to the core loss of the rotary head and so on, much power is required for the signal erasure. On the contrary, if the frequency of the erasing signal is selected low, the magnetization level by the erasing signal recorded on the magnetic tape is high and the wavelength of the erasing signal is long. Accordingly, unless the azimuth angle of the rotary erasing head relative to the recording and/or reproducing rotary magnetic head is selected to be considerably large, due to the azimuth loss, the level of the reproduced erasing signal can not be reduced. In practice, it is not so easy to produce the rotary erasing head having a large azimuth angle so that the level of the reproduced erasing signal can not be reduced so much, thus making an S/N (signal-to-noise) ratio poor and hence deteriorating the picture quality.
In the above case, when a magnetic tape having a high coercive force H.sub.c is used or a tracking pilot signal (a single mode signal with the frequency of 100 to 150 kHz) is recorded together with a video signal, much more erasing power is necessary so that the influence due to the reproduced erasing signal becomes stronger.
In U.S. Pat. No. 4,205,356, there is disclosed a double gap type or semi-double gap type erasing head in which after the erasing, the distortion ratio of the recorded signal can be reduced. However, in U.S. Pat. No. 4,205,356, a relation between the gap and the erasing frequency was not referred to. In view of such aspect, it is considered that more desired erasing could not be attained yet.